Thermal conductivity lattice component

In Solids, heal conduction is due to two effects the lattice vibrational waves induced by the vibrational motions of the molecules po.sitioned at relatively fixed positions in a periodic manner called a lattice, and the energy transported via the free flow of electrons in the solid (Fig. 1—28). The Ihermal conductivity of a solid is obtained by adding the lattice and electronic components. The relatively high thermal conductivities of pure metals arc primarily due to the electronic component. The lattice component of thermal conductivity strongly depends on the way the molecules are arranged. For example, diamond, which is a liighly ordered crystalline solid, has the highest known thermal conductivity at room temperature. 

The thermal conductivity X of metals has two components, an electronic component A and a lattice component for which the phonons are the heat carriers. The electronic component Xe can be written as follows in terms of the thermal resistivity W of the electron system... 

Ar = temperature difference between thermometer stations A = total thermal conductivity Ag = electronic component of thermal conductivity Ag = lattice or phonon component of thermal conductivity Ah = total thermal conductivity at magnetic field H p = electrical resistivity Ph = electrical resistivity at magnetic field H... 

Several other equations are worth noting, because their validity has been tested for glass sphere-polymer composites. Behrens (1968) derived a general expression for thermal conductivity in two-component systems having orthorhombic symmetry for spheres in a cubic lattice, the expression becomes... 

The thermal conductivity (k) comprises electrical component (k ) and lattice component (Kj), k = -e Kj. The is related to the electrical conductivity through the Wiedemann-Franz law. That is... 

By analyzing the temperature dependence of the electrical properties, using our results (Fig. 5) and published data [9,10], another characteristic feature of the structure of CrSi2 crystals becomes apparent, which makes the energy spectrum of valence electrons in this compound more precise. A calculation of the lattice thermal conductivity of single crystals, taken as the difference between the total and electronic thermal conductivities (Fig. 5), as a function of temperature, shows that it decreases continuously up to the maximum measurement temperature. This Indicates the absence of an additional heat transfer component due to ambipolar diffusion of carriers [18] in the intrinsic conduction range. 

The thermal conductivity or k (i.e., the time rate of transfer of heat by conduction) of interstitial carbides is different from that of most other refi actory materials as k increases with increasing temperature as shown in Fig. 4.2.l l Typically, the mechanism of thermal conductivity involves two components electron thermal conductivity and phonon (lattice) conductivity kp. As shown in Fig. 4.3 (in this case for titanium carbide), k increases markedly with temperature. This behavior is believed to be the... 

Fig. It.1-tt6a,b Ge. Thermal conductivity vs. temperature, (a) 3-400 K, (b) 400-1200 K. Solid curve in (a) and data in (b) from [1.40] experimental data in (a) from [1.45]. Dashed line in (b), extrapolated lattice component...

For polycrystalline samples values of the total thermal conductivity X at 293 K, of the electronic component X(el) derived by the Friedemann-Franz law under the assumption that the Lorenz number L = 2.45x 10" V/K as for a degenerate electron gas, and of the lattice component X(lat) obtained by subtraction are, Zhuze et al. [15] ... 

Zhuze et al. [3]. The temperature dependence of is shown in Fig. 36a for -100 to -650 K. The thermal resistivity of the lattice 1/>.iat was determined by subtraction of the normal (calculated) electronic component 1/ iei from the experimental 1/ tot- It showed a decrease at high temperatures whereas theory predicts an increase. This is probably due to an anomalous behavior of the electronic component which is explained by the presence of a complex conduction band, consisting of subbands with heavy and light current carriers. The compound may be considered as a highly doped semiconductor with the Fermi level close to the bottom of the second band. The high values of 1/Xiat observed at low temperatures of -80 to 150 K are attributed to phonon scattering at the levels of the paramagnetic Ce ions split by the crystal field [1]-... 

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